Mill Gibs

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: GlennW, Harold_V

User avatar
seal killer
Posts: 4696
Joined: Sat Aug 18, 2007 10:58 pm
Location: Ozark Mountains

Mill Gibs

Post by seal killer »

All--

This morning I needed to set up a 12"long piece perpendicular to the table. I indicated it from the spindle housing and found I could not get it better than 0.002" along an 8" length of the piece. After screwing with it (for far too long), I grabbed each end of the table and wiggled it back and forth. Sure enough, about 0.002" play.

Gibs? (In the 15 years that I have been learning from you, I never asked about gibs!)

If so, it seems simple enough to adjust them. My manual says to loosen one and tighten the other until a slight drag is felt with the feed. I've never done this so I need to ask about any tips, techniques and/or cautions. I know not to over-tighten the gibs.

Thanks!

--Bill
You are what you write.
User avatar
Bill Shields
Posts: 10464
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: Mill Gibs

Post by Bill Shields »

gibs or wear.....

you can probably tighten it out...but then will the table move full travel?
Too many things going on to bother listing them.
User avatar
Harold_V
Posts: 20232
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Mill Gibs

Post by Harold_V »

seal killer's mill is unlikely to have that much wear. I suspect the simple tightening will eliminate the slop he is experiencing.

Tighten the gib until you feel some drag when the slide is in either (or both) extremes of travel. I suspect that, now, the hand wheel turns effortlessly. You should have a clear understanding once you achieve some drag.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: Mill Gibs

Post by pete »

Since you didn't say I still have to ask to be sure, you do mean for tapered gibs right? How I figured out how to do it was the one screw at the gibs fat end is the only one that's doing the adjustment. Loosen the one at the gibs small end a bit, then start adjusting the other end in as you check the feel of how tight your making that adjustment with the hand wheel. Once you have that light drag feel and no perceptible extra clearance, then run the opposite screw in to lock the adjustment. On my mill there seems to be a little variation on the exact gib adjustment as that second screw gets tight. So you might need play with it back and forth a bit to experiment for what's correct for yours.

15 years and no adjustments? I pull my table every year or two. That allows me to properly clean the ways, screws and nuts, inspect the one shot oiler doesn't have any plugged oil galleys or line restrictor's and the oil is getting everywhere it's supposed to. Then adjust those X,Y nuts for back lash and clean out any chips that somehow get in there. Pull the Y axis screw, clean, adjust it's gib and also the gib on the knee. I use this to spray clean the screws and nuts because of how easy it removes all that old oil and any built up crud. http://crc-canada.ca/qd-8482-contact-cl ... grams.html All this only takes an hr or two once you've done it a few times. And to me this is just standard preventative maintenance. The first time I did this it showed a light score mark starting on one of the ways surfaces. There was an un-noticed slightly high spot on the one of the gibs, stoning the surface removed that and I wasn't all that impressed with it's factory finish either. So I lapped all the gib faces a bit and I think that even improved things some more. Mine always feels smoother with those clean surfaces and fresh oil and I think can be adjusted a tiny bit tighter. But with enough wear as Bill said that gib adjustment if it gets tight at the ends is then a best average. I'd almost bet your not there yet as Harold said.
User avatar
seal killer
Posts: 4696
Joined: Sat Aug 18, 2007 10:58 pm
Location: Ozark Mountains

Re: Mill Gibs

Post by seal killer »

pete and Harold and Bill--

Thank you for the help!

pete, remove the table; now you have me thinking about how to do that. (It will not be this time around, though!) I do not know if the gibs are tapered. My manual, usually pretty good, only has two sentences regarding the gibs.

Harold, you are correct in thinking my mill probably does not have much wear. :) You put that very diplomatically!

Bill, thanks for that tip. I'll make sure I see if it does.

--Bill
You are what you write.
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: Mill Gibs

Post by pete »

The description you used in your OP I was fairly sure but not positive indicated it only has screws on each end, if so that should be a tapered gib. I asked not to confuse things, but just to be 100% sure of what you had Bill. Also I forgot to mention, it depends on the material the gib is made from, it's not impossible to over tighten the slotted screws that lock the gid adjustment setting. I've read a few posts where people have broken the end off the gib on what I think were probably cast iron gibs. Do that and it's pretty much getting a new gib at that point. So tighten but don't reef down on the screw heads like your trying to tighten lug nuts on a tractor.

Removing the table is pretty simple other than it's weight. Easiest for me is on the X axis to just pull each of the components off of each end of the X axis screw including the end screw supports that hold the bearings, loosely reinstall one hand wheel back on, and rotate the screw out of engagement with the nut while supporting the screw as it comes out with your free hand and unscrew until it's clear of the nut. Remove the gib and then slide the table off onto a cart at the correct elevation, use the knee to fine tune what ever elevation works best, or use an engine cherry picker or any other means you have. My mill is what's referred to as a 3/4 sized, or baby Bridgeport with a 9" x 35" table, I'd estimate it's bare weight at around 130-150 lbs. I seem to recall your mill table is a bit larger, so expect maybe quite a bit more weight. If you've got additions like a power feed, dro etc. Then those obviously come off as well. Because of my shop layout, I had zero choice but to pull my mill apart to get it in there without ever having even used a BP type mill first, or having seen one in pieces. Other than mills with built in geared power feeds, there a pretty simple collection of parts. If I can do it anyone can. :-) Just lay the parts out on a clean surface in the order of removal, and keeping everything in there as removed left or right hand orientations like those hand wheel and dial assembly's. The Y axis screw is even more simple. There "should" be alignment pins of some type on those end supports that hold the bearings the X axis screw rotate on. Just in case there isn't on your mill? Install everything back together and leave a turn or two loose on the bolts that fasten the supports to each end of the table. Then run the table in on the X axis as far as it will go in one direction. Only then fully tighten the bolts on that end. That way the nut has self aligned the bearing supports to the nuts C/L. Then do the opposite end in the same way. I suspect on yours though there will be the standard alignment pins. If you don't do the alignment in that way when there's no pins you'll almost for sure get table binding at the ends of the table movement and massive wear on the nuts. Because of that misalignment, the nut is literally trying to bend the screw back into alignment which it can't do.
User avatar
seal killer
Posts: 4696
Joined: Sat Aug 18, 2007 10:58 pm
Location: Ozark Mountains

Re: Mill Gibs

Post by seal killer »

pete--

That post is a keeper, for sure.

I have some very good surfaces onto which I can slide the table.

In my ignorance, I thought there were gibs on both sides of the knee. Upon reading your post, I see that there is one gib on the knee; I just went into the shop, removed the wiper on the rear and a plate on the front and saw that the gib on my machine is on the same side as the lock handles.

That would have become apparent when I actually go to adjust it. But now I have the picture. I believe I will have some shop-time tomorrow. The first thing to do is to adjust that gib.

Thank you!

--Bill
You are what you write.
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: Mill Gibs

Post by pete »

Well because of the vertical orientation on that knee gib, I'll double my caution about being careful with tightening it Bill. There's been a few posts on the PM forums of people that for a few reasons broke that gibs large end off and then tried to move the knee up. From those posts you DON'T ever want that issue. What happens is the loose end of the gib then wedges itself in there and makes the knee totally immobile. It then refuses to go up or down no matter how much force is applied to the knee crank. And the more force you apply, the tighter that loose end of the gib wedges itself in there making it far, far tougher to ever get it out. One poster from memory mentioned working on his off and on for over three weeks with zero progress. And just to get at least some easier access, the head, ram, table, assembly really needs to come off, and the mill column laid on it's back. If it's really stuck, trying to drive the gib end back up and out with punches either chips out pieces with cast iron gibs or begins to peen over the gib end making it even tighter. I'd suggest it's one of those life experiences best read about instead of living through. :-)

Proper adjustment of that knee gib is a bit more complicated. Yes you want minimum of clearance, but it's a bit harder to tell what's correct or not because of the knee,table assembly's total weight. And due to that, the knee can sag a bit in the forward direction away from the column. And with all the weight it tends to feel like there's some drag feel present as it moves up/down, but in fact the gib adjustment could be a bit loose. No matter how well any gibs are adjusted to remove as much clearance as possible, you still have to have at least some to allow a slide to even move, plus have a bit for oil clearance between the parts. I still use that feel on the knee crank as the adjustments are being made, but as a double check I'll usually use some blocking in front of the knee and then use about a 3'-4' length of 2"x 4" to pry the knee up with an indicator on and towards the front edge of the table. If it does start feeling tight using the knee crank, I then know the last adjustment was a bit too much. Even with the exact correct adjustment made on that gib, you'll see at least some movement on the indicator while prying the knee casting up because of the non optional clearance you have to have. Your just trying to get it to the bare minimum while not being too tight. Maybe real machinist's wouldn't need to do it this way, but I want to know if there's any excess clearance that's allowing the knee to sag forward more than it should be. And if that knee gib does need adjusting, it's almost for sure your spindle tram will then be a bit off in the Y axis after that's done because tightening up the clearance will pull the slides together more, but also the angle on the dovetails moves and tilts the knee further back and more into contact with the flat vertical way surfaces. A bit hard to describe properly, but I hope you got the visualization of what happens.

Just as further general information, I don't know of any machine tool that uses a gib on each side. One is all you need because that helps pull the slides dovetail into contact with the opposite and solid dovetailed or box way side, and I've seen that referred to as the master or main alignment surface. It's not really pertinent to a mill. But there's definite reasons why the gibs are placed where they are on something like a lathe. There always placed on the opposite side where in general the cutting loads are generated and help force the slides into solid contact. If the gibs were on the opposite side, then those loads would tend to increase the clearance more. A small detail, but they do have those definite and logical reasons for the gibs at least on lathes being placed where they are.
RSG
Posts: 1541
Joined: Fri Feb 04, 2011 9:59 am
Location: Ontario, Canada

Re: Mill Gibs

Post by RSG »

Great reply Pete! Thanks!
Vision is not seeing things as they are, but as they will be.
User avatar
seal killer
Posts: 4696
Joined: Sat Aug 18, 2007 10:58 pm
Location: Ozark Mountains

Re: Mill Gibs

Post by seal killer »

pete and All--

pete, first, a correction: I wrote "knee" but should have written "cross feed."

I loosened both gib screws a bit, then tightened one. I never felt any difference in the feed. I kept screwing with it. Eventually, I decided to switch ends by screwing the other end in to tighten it and then locking it down with the opposite screw.

I never felt any difference. However, I remembered the advice about not torqueing it down really tight.

I put the Kurt on to use the side as a straight surface to indicate against. Well, that was a bust as the Kurt appeared to have a few thousands bulge in about the center of the side. Hmmm. What to use?

I grabbed a 6" parallel and indicated it in. Within that six inches, my dial indicator stayed rock solid. So I moved the parallel towards me to get the rest of the measurement. Still rock solid.

I think I'm good. However, I am going to buy a foot long (or at least 9" long) high quality parallel and repeat all this.

But I am feeling better about the mill.

--Bill
You are what you write.
User avatar
Bill Shields
Posts: 10464
Joined: Fri Dec 21, 2007 4:57 am
Location: 39.367, -75.765
Contact:

Re: Mill Gibs

Post by Bill Shields »

and when it was brand new...what was the end - to - end runout?
Too many things going on to bother listing them.
User avatar
seal killer
Posts: 4696
Joined: Sat Aug 18, 2007 10:58 pm
Location: Ozark Mountains

Re: Mill Gibs

Post by seal killer »

Bill--

Re: "and when it was brand new...what was the end - to - end runout?"

No clue. :(

--Bill
You are what you write.
Post Reply